My 3 year old cat had surgery to repair her torn ACL two years ago. We would let her outside for a few hours while we watched her and we did not think she left the backyard. We were wrong! She got into the neighbors yard and climbed a tree but then was too scared to come down. My husband grabbed a ladder and went to rescue her but she freaked on the way down and I guess she lost her balance. She is already a 3-legged cat - missing her front right paw - and the fall was too much for her back left leg and her ACL completely tore. It was heartbreaking! I did not know how she would survive being down to 2 legs even if just for a bit.
But she got surgery the next day and the vet assured me she was never in any pain. My vet also said this is a rare incident for cats, and the first time ever for a 3-legged cat, so my little girl made history and science books! We had to crate train her for a few months, and that was also hard at first. She would cry all night long. But after about a week, she would go in her crate when she knew we were leaving for work and eventually it became her favorite place. We had to leave it up for almost a year after she healed! And when we took it down, we did it piece by piece. She had a cardboard litter box in there with her, but she preferred to use it as a bed. We still have it out in her corner and it is still her favorite place!
She completely recovered, but we watch that leg like crazy and she is not allowed to go too high! We call that leg her "$1500 leg"! and that does not even cover all the cost! But of course, she is worth every penny.